1. Field of the Invention
This invention relates to manufacturing methods for organic electroluminescence (EL) devices, and also relates to electronic devices using them.
This application claims priority on Japanese Patent Application No. 2003-15102 and Japanese Patent Application No. 2003-308968, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In general, organic electroluminescence (EL) components adapted to organic electroluminescence devices have structures in which organic luminescent materials are arranged as thin films sandwiched between anodes and cathodes (or positive electrodes and negative electrodes), wherein electrons and holes injected by both electrodes are reunified in luminescent layers, thus causing excitation of energy to emit light. These organic electroluminescence devices have relatively high charge injection barriers between electrodes and luminescent layers. For this reason, they normally use the laminated structure comprising hole transport layers (or hole injection layers) serving as anode buffer layers and electron transport layers (or electron injection layers) serving as cathode buffer layers. In this laminated structure, the electron transport layer is in particular composed of lithium fluoride (LiF) or magnesium oxide (MgO), whereby it is possible to produce an organic electroluminescence device actualizing low-voltage drive. This is disclosed on page 152 of Applied Physics Letters, Vol. 70 (1997), for example.
Presently, organic luminescent materials used for electroluminescence devices are mainly classified into two groups, namely, a low-molecular group and a high-molecular (or polymer) group. Organic luminescent materials of the low-molecular group are normally subjected to the gaseous phase process such as vacuum evaporation to form thin films, which are then subjected to patterning using masks. This is disclosed on page 34 of Applied Physics Letters, Vol. 51 (1997), for example. Organic luminescent materials of the polymer group can be dissolved in solvents, so that they are subjected to the application method (or coating method) to form films, which are then subjected to patterning by the liquid-drop discharge method such as the inkjet method. This is disclosed on page 34 of Applied Physics Letters, Vol. 71 (1997), for example. Manufacturing methods for an organic electroluminescence device formed by the liquid-drop discharge method are known, an example of which is disclosed in Japanese Patent Application Publication No. Hei 10-12377.
Materials that can be subjected to the application method to form film have been developed with respect to hole transport layers serving as anode buffer layers, which allows formation of films by a gaseous process. This is disclosed in the article on page 477 of Nature, Vol. 357 (1992).
The vacuum evaporation method is normally used for the formation of films with respect to electron transport layers serving as cathode buffer layers. However, this may increase the manufacturing cost in terms of energy consumption and supply of materials. In addition, this may cause an unwanted factor interfering enlargement of sizes of substrates for organic electroluminescence devices, which will be practically used and incorporated into displays in the future. When organic electroluminescence devices are formed by the gaseous process, organic substance beds or substrates must be exposed to high-temperature environments; therefore, various problems such as deterioration of luminescence characteristics and deformation of substrates may occur in the case of prescribed materials having poor heat resistance.
When electron transport layers are formed on luminescent layers in the liquid phase, luminescent layers serving as beds therefor must be dissolved due to some solvent actually used.
Various examples have been developed with respect to the formation of cathode buffer layers (serving as electron transport layers) in the liquid phase process. For example, Japanese Patent Application Publication No. 2000-252076 discloses the method in which layers are formed by the wet method using polymers having electron transportability (where one to five alkyl or alkoxyl elements are included in each repeat unit) that are dissolved or dispersed. In addition, Japanese Patent Application Publication No. 2000-252079 discloses the method in which electron injection layers are formed by the wet method using the solution (or dispersed solution) in which tetrahydro-aluminate elements are dissolved or dispersed.
The conventional examples regarding the formation of electron transport layers in the liquid phase process fail to disclose the formation of electron transport layers that are formed in the liquid phase process using alkali metals and alkali earth metals, which produce good results in the conventional gaseous process, as well as halides (e.g., LiF) and oxides of rare earth metals.